Toxicity was compared among four tall fescue clone pairs. Seasonal comparisons were made by measuring development of fruit flies, Drosophila melanogaster Meigen, in diets prepared with endophyte-infected (E+) and endophyte-free (E-) tall fescue leaf powder. Toxicity was also evaluated by observing the behavior of the corn flea beetle, Chaetocnema pulicaria Melsheimer, on E+ and E- tall fescue leaf segments.
Clone pairs developed at The University of Tennessee were designated as 31, 38, 39 and 48. Diets containing 38E+ tall fescue had less fruit flies than other diets during most of the year. Diets containing 39E+ tall fescue had fewer fruit flies than other diets in summer. Diets containing 31E+ had more fruit flies than other E+ diets in spring. Toxic effects of all E+ diets diminished in winter.
In no-choice bioassays, corn flea beetles were found on E- tillers more often than all E+ tillers except 39E+. Amount of feeding was similar on E+ and E- tillers of clone pair 39; whereas, E+ tillers of other clones had less feeding than the respective E- tillers.
Since contrasting levels of toxicity occur in E+ plants, a variety of phenotypes may be expected in a pasture. Results of this study show the importance of evaluating several clone pairs before a particular variety is selected for livestock forage
